in reply to Re^2: Formatting a number
in thread Formatting a number

Problem with that is the length is increasing as you insert commas from the right so it needs to be tested dynamically. Unfortunately, your modification breaks the routine.

use strict;
use warnings;

my @nos = qw{
   1
   12
   123
   1234
   12345
   123456
   1234567
   12345678
   123456789
   1234567890
   12345678901
   123456789012
   1234567890123
   12345678901234};

printf qq{%20s\n}, useSubstr($_) for @nos;

sub useSubstr
{
    my $number = shift;
    my $length = -( 1 + length $number );
    my $offset = -3;
    while ( $offset > $length )
    {
        substr $number, $offset, 0, q{,};
        $offset -= 4;
    }
    return $number;
}

[download]

produces

                   1
                  12
                ,123
               1,234
              12,345
             123,456
           1,234,567
          12,345,678
         123,456,789
        1234,567,890
      12,345,678,901
     123,456,789,012
    1234,567,890,123
   12345,678,901,234

[download]

As you can see, it breaks out of the while too soon as it has not kept up with the increasing length of the number as the commas go in. I agree that it would be nice to factor abs and length out of the loop but can't quite see how to achieve it.

Cheers,

JohnGG

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Re^4: Formatting a number
by jwkrahn (Abbot) on Oct 17, 2006 at 15:14 UTC
    Right, I didn't test very much.   :-) This works correctly and appears to be about 10% faster: 
    
sub useSubstr { 
    my $number = shift;
    my $len = length $number;
    my $offset = 3;
    while ( $offset < $len ) {
        substr $number, -$offset , 0, q{,};
        $offset += 4;
        $len = length $number;
        }
    return $number;
    }

    [download]
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      Nice ++. I don't know why I couldn't suss that one out myself. Perhaps I'd worn my brain out :(
[reply]

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